Air-blast switch with safety valve



Feb. 16, 1960 H. THOMMEN AIR-BLAST SWITCH WITH SAFETY VALVE Filed May 9. 1958 United States Patent O AIR-BLAST SWITCH WITH SAFETY VALVE Hans Thommen, Baden, Switzerland, assignor to Aktiengesellschaft Brown, Boveri & Cie, Baden, Switzerland, a joint-stock company Application May 9, 1958, Serial No. 734,319

Claims priority, application Switzerland May 14, 1957 1 Claim. (Cl. 200-148) This invention relates to electrical switch means, and is concerned more particularly with improvements in power switches equipped with arc extinction chambers.

When switching power switches, a high pressure is generated in the extinction chambers where the contacts are housed. The high pressure is produced by the electric arc itself, which generates gases. If these switches are blasted with compressed air to extinguish the arc, the above mentioned pressure is added to the pressure of the extinguishing air. The extinction chamber must then be so designed that it can withstand the pressure produced at the circuit-breaking capacity.

In switches for maximum voltages such extinction chambers are arranged on insulators, and the compressed air is conducted through one of these insulators. Several such extinction chambers with switching points are provided, which chambers can be supplied with compressed air by a common insulator. The pressure generated in the extinction chambers exists, then, also in the feed insulators.

With circuit-breaking powers in an amount up to the guaranteed circuit-breaking capacity, these parts of the switch` must withstand satisfactorily the occurring overpressures. The parts cannot be destroyed nor can there be any damages at all in such cases.

It cannot be avoided, however, that the circuit-breaking powers actually occurring in the mains exceed occasionally the circuit-breaking capacity under particularly unfavorable conditions. In this case it is at least desirable if the switch is not destroyed by the particularly high pressure. This is not ensured in the known models. It is then necessary to replace at least parts of the switch after these switchings.

In order to avoid these disadvantages it is proposed according to the present invention to equip the extinction chambers and the feed lines for the compressed air with safety valves which are adapted to respond if the pressure becomes too high, allowing air and harmful gases to escape. This measure protects the air-blast switch even if the arc does not break off, due to a too high load, but remains. The pressures are then at least not too high, so that the contacts are burnt off to a great extent, but the chambers themselves remain undamaged.

In such cases high temperatures are also produced, which can be eliminated or at least reduced by opening the safety valves. The high temperature itself can also be utilized to actuate the safety valve. This measure is also applicable in switches which are not blasted with compressed air and where there is therefore only a pressure generated by the electric arc. In such cases the safety valves are then provided with thermal members of known design, for example, bimetal releases which Patented Feb. 16, 1960 ice disengage a pawl and then open the valve by means of a spring.

Instead of safety valves diaphragms can also be used, which diaphragms break when the pressure becomes too high or detach themselves at too high temperatures. These diaphragms can be soldered into an easy melting metal, for example, tin, which melts through when the temperatures become too high. At high pressure the diaphragm breaks; at high temperatures the surrounding tin melts.

The invention will now be described in greater detail, and with reference to the accompanying drawing, in which:

Fig. 1 is a diagrammatic view of one form of electrical switch means, including associated arc-extinguishing chambers, showing an application of principles of the present invention;

Fig. 2 is a sectional view showing the application of the diaphragm.

In Fig. 1 reference number 1 indicates the extinguishing chamber and 2 and 3 are the contacts which together form a nozzle-type contact where the hollow contact 3 is arranged to be movable and presses against the spring 4 when the switch is opened. The extinguishing chamber 1 is provided with a safety valve 5 in which the piston 6 compresses the spring 7 when the pressure becomes excessive. A thermal safety valve 8 operates when the temperature becomes too high; its piston is moved in the upward direction by a tension spring 9 when the latch 10 is withdrawn. This withdrawal is effected by the bimetal strip 11 which bends when the temperature reaches a certain value.

Fig. 2 shows a diaphragm 12 which is also built into the wall of the extinguishing chamber. This diaphragm is supported in a metal 13 having a low melting point. When these metal supports melt the diaphragm is forced out and the high pressure gas can escape.

I claim:

An air-blast switch in which the compressed air necessary for actuating and extinguishing the switching points is supplied through hollow insulators and the switching points are arranged in hollow insulators designed as extinction chambers and in which the extinction chambers are equipped with safety valves which respond at excessive pressure allowing air and harmful gases to escape, characterized in that a safety thermal actuating member is located in operative association with an aperture in a wall of an extinction chamber of the switch, said safety thermal actuating member consisting essentially of a piston normally closing said aperture, spring means biased to urge the piston out of closing position in the aperture, and latch means including a bimetal element normally latching said spring means and bending, when heated to a predetermined temperature, to unlatch and release said spring means.

References Cited in the tile of this patent UNITED STATES PATENTS 1,336,069 Conrad Apr. 6, 1920 1,670,697 Treanor May 22, 1928 2,459,599 Strom Jan. 18, 1949 2,838,650 Lehr Jan. 10, 1958 FOREIGN PATENTS 1,104,071 France June 8, 1955 

